A new study conducted by Duke University researchers is the first to link hydraulic fracturing, or fracking, with methane contamination of drinking water wells. According to a report from ProPublica, in some cases, the methane contamination documented by the study was so severe, it caused tap water to burst into flames.

The new study will be published in the Proceedings of the National Academy of Sciences. In conducting the study, the researchers collected and analyzed water samples from 68 private groundwater wells across five counties in northeastern Pennsylvania and New York, which set atop the natural gas-rich Marcellus Shale formation. While the scientists found measurable amounts of methane in 85 percent of the samples, they also found that levels were 17 times higher on average in wells located within a kilometer of active fracking sites. They also found that the type of gas detected at high levels in the water was the same type of gas that energy companies were extracting from the ground.

According to ProPublica, the average concentration of the methane detected in the water wells near drilling sites fell within a range that the U.S Department of Interior says is dangerous and requires urgent â€œhazard mitigation.â€

“At least some of the homeowners who claim that their wells were contaminated by shale-gas extraction appear to be right,” Robert B. Jackson, Nicholas Professor of Global Environmental Change and director of Duke’s Center on Global Change, said in a statement announcing the study results.

The study found no evidence of contamination from fracking fluids, the cocktails of water, sand and chemicals that are injected into the gas wells under high pressure to shake loose gas deposits from shale formations. Nor did they find evidence that “produced waters” – wastewater that is extracted back out of the wells after the shale has been fractured – had tainted water wells.

Methane is flammable, can cause an explosion, and – in very high concentrations – can cause asphyxiation. Methane is not known to be hazardous to drink, though research is limited, ProPublica said.

According to the ProPublica report, other gases were also found in water wells located near fracking sites. For example, ethane, another component of natural gas, and other hydrocarbons were detected in 81 percent of water wells near active gas drilling, but in only 9 percent of water wells further away. Propane and butane were also detected in some drilling area wells.

The publication of the new study elicited a strong response from environmentalists. Dr. Tom Jiunta, president and founder of Pennsylvaniaâ€™s Luzerne County-based Gas Drilling Awareness Coalition, told The Times Leader that the findings should prompt the state’s governor, Tom Corbett, to impose a moratorium on fracking

â€œGov. Corbett said last week he would rely on science, not emotionâ€ for making decisions related to natural gas exploration. â€œThereâ€™s plenty of science out there now, and I think this proves it,â€ Jiunta said.

“It comes as no surprise that natural gas is not as clean as the industry pretends,” Deborah Goldberg, an attorney with Earthjustice, told the Christian Science Monitor.